To improve network reliability, a communication system that provides a physical redundant route between arbitrary bridge devices on a ring network is used. In the ring network, the relay of a data frame through a given port is blocked to perform normal communication and prevent looping of the data frame.
As a result, a relay path between communication apparatuses is uniquely determined. When failure occurs in a line connecting communication apparatuses, the blocking point of the data frame is dynamically changed to restart communication using a path where no failure has occurred. Consequently, a relay path between the communication apparatuses is maintained even if a failure occurs (see, e.g., Japanese Patent No. 3285138).
With a primary aim of expanding band used in a ring network, a technology that connects plural lines (physical lines) between communication apparatuses and uses these lines as one logical line based on link aggregation (LA) specified in IEEE802.3ad is used.
In the link aggregation, when failure occurs in a line among plural lines connecting two communication apparatuses, a technology that performs logical switching by resetting the relay path using lines where no failure has occurred is disclosed in Japanese Laid-open Patent Application No. 2006-262291. According to the technology, the relay path between the communication apparatuses is maintained even if failure occurs.
However, the technology that dynamically changes the blocking point and switches the relay path to a path where no failure has occurred has a problem in that communication is completely disrupted when another failure occurs in the relay path after the switch. Therefore, there is a problem in that tolerance against multiple failures in the ring network is low.
According to the technology that performs logical switching by resetting the relay path using lines where no failure has occurred, since communication continues through fewer lines, communication speed in the relay path is reduced. Therefore, there is a problem in that band increased based on the link aggregation cannot be effectively exploited.